数据结构学习笔记——stack实现（数组篇）

一 栈：是一种表，限制插入和删除只能在一个位置，也即是表的末端（也是栈的顶）进行。

基本操作：push 和 pop。

二 栈的数组实现：

运用数组来存储元素，和栈操作先关的是theArray（一个数组实例）和topOfStack（指向栈顶元素，对于空栈，它的值是-1）。

push操作：将某个元素 item 推入栈中，使得 topOfStack 增1然后置 theArray[topOfStack] = item.

pop操作： 将栈顶严肃弹出，我们置返回值为 theArray[topOfStack]，然后 topOfStack 减1.

三 时间复杂度：

显然都是常数时间运行，O(1)。

java代码实现：

 package com.xuyunyu.demo;
 /**
  *
  * generic type class MyStack to implement the stack with array
  * @author Administrator
  *
  * @param <AnyType>
  */
 public class MyStack<AnyType>
 {
     /**
      * the capacity of the stack
      */
     private static  final int DEFAULT_CAPACITY = 10;
     /**
      * the array to store the elements
      */
     private AnyType[] theItems;
     /**
      * the pointer to point to the top of the stack
      */
     private int TopOfStack;
     /**
      * constructor
      *
      * to initial the stack
      */
     public MyStack ()
     {
         clear();
     }
     /**
      * clear the stack
      */
     public void clear()
     {
         theItems = ( AnyType [] ) new Object[DEFAULT_CAPACITY];
         TopOfStack = -1;
     }
     /**
      * get the capacity of the stack
      * @return
      */
     public int size()
     {
         return DEFAULT_CAPACITY;
     }
     /**
      * get the actual counts of
      * the element stored in the stack
      * @return
      */
     public int getCountOfElement()
     {
         return TopOfStack + 1;
     }
     /**
      * get the top element of the stack
      * @return
      */
     public AnyType getTopElement()
     {
         return theItems[TopOfStack];
     }
     /**
      * judge if the stack is empty
      * @return true if the stack is empty,false or not
      */
     public boolean isEmpty()
     {
         return TopOfStack == -1;
     }
     /**
      * judge if the stack is full
      * @return true if the stack is full,false or not
      */
     public boolean isFull()
     {
         return (TopOfStack + 1) == theItems.length;
     }
     /**
      * push an item to the stack
      * the TopOfStack INC ,and then store the item
      * @param item
      */
     public void push(AnyType item)
     {
         if(isFull())
             throw new IndexOutOfBoundsException();
         TopOfStack++;
         theItems[TopOfStack] = item;
     }
     /**
      * return the item on the top and then make one decrement of the TopOfStack
      * @return
      */
     public AnyType pop()
     {
         if(isEmpty() )
             throw new IndexOutOfBoundsException();

         AnyType ItemPulled = theItems[TopOfStack];
         theItems[TopOfStack] = null;
         TopOfStack--;
         return ItemPulled;
     }

 }

注意：这是一个泛型类，更加具有复用性。

四 测试代码：

 package com.xuyunyu.demo;

 public class test_MyStack
 {
     public static void main(String[] args)
     {
         MyStack<Integer> stack = new MyStack<Integer>();
         System.out.println("counts of the stack: " + stack.getCountOfElement());
         System.out.println("size of the stack: " + stack.size());
         //System.out.println("top element of the stack: " + stack.getTopElement());

         stack.push(17);
         System.out.println("counts of the stack: " + stack.getCountOfElement());
         System.out.println("top element of the stack: " + stack.getTopElement());

         stack.push(30);
         System.out.println("counts of the stack: " + stack.getCountOfElement());
         System.out.println("top element of the stack: " + stack.getTopElement());

         stack.clear();
         System.out.println("counts of the stack: " + stack.getCountOfElement());

         System.out.println("push to the stack:" );
         for (int i = 0; i < stack.size(); i++)
         {
             System.out.print(" " + i);
             stack.push(i);
         }
         System.out.println();

         System.out.println("pop from the stack:" );
         for (int i = 0; i < stack.size(); i++)
         {
             System.out.print(" " + stack.pop());
         }

     }

 }

期待输出如下：

counts of the stack: 0
size of the stack: 10
counts of the stack: 1
top element of the stack: 17
counts of the stack: 2
top element of the stack: 30
counts of the stack: 0
push to the stack
 0 1 2 3 4 5 6 7 8 9
pop from the stack
 9 8 7 6 5 4 3 2 1 0

结论：

显然实现了stack的后进先出的性质。

栈可以应用到平衡符号，中缀到后缀的转换以及方法调用上。详情可参考Mark Allen Weisss的《数据结构与算法分析——java语言描述》。 本文部分内容页参考此书。